The cross-bolt spacing on DigitalHunter is designed to interface with the standard military mounting rail for small arms weapons (MIL-STD-1913). It is very strong mount that uses .190 Diameter cross bolts. It was developed at the Picatinny Arsenal, NJ, and is commonly referred to as a Picatinny rail. DigitalHunter has 5 cross-bolt mounting holes on each end with a blank space in the middle equal to 4 holes. This is the equivalent of 14 equally spaced holes with 13 spaces between them. Using the the pitch dimension (distance between bolts) of .394 inches you can calculate the distance between any number of holes. For example: The first and last bolts are 5.122 inches apart (13 X .394). Likewise, any bolt spacing can be determined. Weaver™ and similar rails may be modified by a machinist or gunsmith (to replace the Picatinny rail) by adding or enlarging existing slots (.206 inch slot width) to the specified dimensions. Potential sources for Picatinny rails are: